Charging of photo-conductive insulating material



April 18, 1961 J. 1 TREGAY ETAL CHARGING OF PHOTO-CONDUCTIVE INSULATING MATERIAL Filed April 26, 1956 INVENTORS John L. Tfegay Joh/z JSC/za je BY ATTORNEY United States Patent() ice CHARGING F PHOTO-CONDUCTIVE INSULATING MATERIAL Filed Apr. 26, '1956, Ser. No. 580,892

2 Claims. (Cl. S17- 262) This invention relates to process and apparatus for producing an electrostatic charge upon the surface of a photo-conductive insulating material, such, for example, as paper coated with a nely divided photo-conductor, e.g., zinc oxide applied to the paper as a solution or suspension in a dielectric lm-formingvehicle- -The vehicle may be a resin solution or suspension, such as a solution of a silicone resin in a suitable solvent or a suspension of a polyvinyl acetate resin in an aqueous medium. Since this invention may be applied to the production of electrostatic charges on any type of photo-conductive 'msulating material, it is believed that further description thereof is not necessary Afor a proper understanding of the invention.

Heretofore the charging of photo-conductive insulating material has been eiected by corona discharge needles 0r wires. Such charging procedures have several disadvantages among which may be mentioned:

(1) The corona discharge needles or wires, being exposed to the atmosphere, generate ozone which escapes into the surrounding atmosphere so that it is objectionable to the operators of the equipment.

(2) The corona discharge wires or needles are delicate and hence readily inadvertently damaged in the operation of the equipment.

(3) When it is attempted to charge a photo-conductive insulating material while in contact with the translucent original it is invariably diiicult to get a uniform charge because of poor contact between the translucent original and the photo-conductive insulating material.

(4) In prior procedures in an eort to produce a uniform charge, the photo-conductive insulating material is fed under the corona discharge and the translucent original then placed on the charged sheet before exposure. This registration of the original on the charged sheet is diicult particularly in hand operated machines.

Itis an object of the present invention to provide process and apparatus for charging photo-conductive insulating material, which method and apparatus do not involve the above noted disadvantages.

Another object of the present invention is to provide a simple and compact charging apparatus for applying a l uniform charge, which apparatus is eicient in operation and can be used to charge photo-conductive insulating material varying in width.

Still another object of the present invention is to provide charging apparatus for charging photo-conductive insulating material uniformly and at relatively high rates of speed.

Still another object of the present invention is to provide charging apparatus which will efficiently and uniformly charge photo-conductive insulating material while in contact with a translucent original and which insures good contact between the translucent original and the photo-conductive insulating material.`

Still another object of the present invention is to provide charging apparatus which does not involvethe use of a fragile corona wire and in the operation of which less Patented Apr. 1s, 1.961

ozone is generated than in prior known equipment involving the use of au open corona wire or corona discharge needles.

Other objects and advantages of this invention will be apparent from the following detailed description thereof:

In accordance with this invention, photo-conductive insulating material is charged by passage, desirably but not necessarily, in contact with a translucent original, between two cylindrical surfaces,v one of which is a grounded conductive surface and the other of which is a semi-conductive surface having a resistance within the range of 1 to 20,000 megohms per cubic centimeter, measured at 8,000 volts per centimeter, while applying a voltage of from 500 to 10,000 volts, preferably from about 4000 to 6500 volts, to the semi-conductive surface.

The semi-conductive surface, we have found, allows the current to pass therethrough and charge the photoconductive insulating material, but has enough resist- `ance to prevent local discharge between the cylindrical surfaces at the edges of the photo-conductive insulating material. Hence, the present invention can be used to charge photo-conductive insulating material varying in width and of any desired width; the length of the cylindrical surfaces are so chosen as to permit the charging of photo-conductive insulating material of maximum width.

In the accompanying drawing, forming a part of this specification, and showing, for purposes of exemplication, a preferred form of this invention, without limiting the claimed invention to such illustrative instance;

Fig. 1 shows partly in section and partly in elevation, a preferred embodiment of this invention. This figure shows a vertical section through the charging roll and shows the cooperating feed roll in elevation; and

Fig. 2 is a section taken in the plane indicated by line 2 2 on Fig. 1.

ln the drawing, 10 indicates a charging roll comprising a steel or other electrically conductive material core 11, provided with shafts 12, 13, also of steel or other electrically conductive material. Shafts 12 and 13 are `suitably journaled for rotation in electrically nonconductive bearings 14 and 1S mounted on the frame 16 of the machine. The bearings 14 and 1S may be of nylon or other suitable non-conductive material. A non-conductive bushing 17, desirably of nylon or other suitable non-conductive material, is xed to shaft 13 and has keyed thereto a drive sprocket 18 which may be driven, for example, by drive chain 19, actuated from any suitable source of power, such as an electric motor, not shown. Brush 21 is in electrical contact with one end of shaft 12. This brush communicates through an electrical conductor 22 with the positive terminal 23 of a high voltage generator 24, the negative terminal 25 of which may be grounded, as indicated at 26. The showing of the drawing is, of course, exemplary, and shows the connections to the high voltage generator for applying a negative charge to the photo-conductive insulating material when the sheet is run coated side up. If it is desired to apply a positive charge, the negative terminal 25 is connected to the brush 21 and the terminal 23 grounded. If the sheet is run coated side down, the charge is reversed on the photo-conductive surface.

High voltage generator 24 may be any known type of high voltage generator, such, for example, as a transformer-rectier system, capable of providing the high voltage to the core 11, say, Within the range of from. 500 to l0,000 volts or higher, preferably from about 4000 to 6500 volts. As such generators are well known, further description thereof is believed unnecessary. I i f: YCore 11 is covered with a layer 27 of semi-conductive material having a resistance of from l to 20,000 megohms, preferably from 500 to 1500 megohms per cubic centimeter, when measured at 8,000 volts per centimeter. The preferred material is a semi-conductive rubber, natural or synthetic, having the resistance properties noted. Such rubber is available commercially, usually containing carbon black, the conductivity depending on'the carbon black content. Examples of such Yrubbers are Cornpound #365-10, manufactured by Dearborn Rubber Corporation, Chicago, Illinois, and Compound #GRM-7, manufactured by W. H. Salisbury and Company, Chicago, Illinois.

Instead of rubber, other semi-conductive materials having the resistance properties noted may be used, such as Synthane synthetic resin (synthetic tar acid resin) containing uniformly dispersed graphite, manufactured by Synthane Corporation, Oaks, Pennsylvania, or the material known as lndox 1 Ceramic, which is chieiiy a mixture of barium carbonate and iron oxide, and is manufactured by The Indiana Steel Products Company, Valparaiso, Indiana.

The semi-conductive covering may be in thc form of a tube snugly engaging the periphery of the core 11; the wall thickness of this tube in the case of rubber is about 5 mm.

Cooperating with the charging roll is a feed roll 28 mounted for rotation in suitable guides 29 on the frame t6 just above the charging roll 10. Feed roll 28 is thus grounded to the frame of the machine. This roll may be of metal or other suitable electrically conductive material. it is so positioned relative to the charging roll l0 that the weight of roll 28 exerts pressure on the sheet of photo-conductive insulating material 30 and the translucent original 31 fed by these rolls. While in the embodiment of the invention shown in the drawing, feed roll 28 is mouned above charging roll 10 in the guides 29, desirably of channel shape, so that it is maintained in contact with charging roll 10 by gravity, it will be understood a spring pressure mounting for feed roll 2S may be employed. In this Way, a sheet of photoconductive insulating material alone, i.e., without the associated translucent original, or the assembly of both sheets, may be fed without requiring any adjustment of the position of the feed roll 28 relative to the'charging roll l0.

It will be noted that sheets of varying width, narrower than the length of the charging roll 10, can be charged. The length of roll 10 and cooperating feed roll 28 is so chosen as to charge sheets of maximum width. Since the resistance of layer 27 on the charging roll 10 is enough to prevent local discharge between charging roll 10 and feed roll 28 at the edges of the photo-conductive insulating material fed between the two rolls, sheets varying in width may be charged uniformly, rapidly and efficiently.

In the operation of the apparatus, the charge is uniformly applied to the surface of the photo-conductive insulating material; the charging roll 10 and the cooperating feed roll 2S provide intimate contact between the photo-conductive insulating material and the surface of the charging roll 10 and also between the photoconductive insulating material and the associated translucent original, when such assembly is fed through the charging apparatus, permitting charging at relatively high speeds.

lt will be understood that the polarity of the charge applied to the photo-conductive insulating material and the relative positions of the translucent original and the photo-conductiveinsulating material may be varied as desired, i.e., the photo-conductive insulating material may contact either the periphery of the charging roll l0 or of the feed roll 23, and. similarly, the translucent original may either contact theperiphery of the feed roll 28, as shown. or be placed beneath the photoconductive insulating material, and thus contact the, periphery of the charging roll l0. When thetranslucent original is in surface contact with the charging roll 10, the charge passes therethrough and collects uniformly 4 on the surface of the superimposed sheet of photoconductive insulating material.

In the operation of the charging apparatus of this invention, it is only necessary to feed the leading end of each photo-conductive insulating sheet or assembly of such sheet with the translucent original to be copied, into the bite between the charging roll 10 and the feed roll 28. Feed roll 28 maintains the sheet or assembly in contact with the periphery of charging roll 10, in the case of the assembly, with good contact between the two sheets. Uniform charging of theV photo-conductive insulating sheet takes place as a single sheet or assembly is fed through the two rolls. Uniform prints result when the electrostatic latent image produced upon exposure to the light is developed by the application of a developer powder, as is well known in the art.

It will be noted that the present invention provides a charging apparatus not requiring the use of a fragile corona wire. ln operation, it has been found that less ozone is generated than in the heretofore known charging apparatus involving corona wires disposed in the atmosphere, i.e., open corona wires or corona discharge needles. Moreover, the charging apparatus of this invention permits the uniform charging of the photo-conductive insulatnig sheet, while in contact with the translucent original, so that the two sheets can be placed in registry and the resultant assembly fed through the charging apparatus, thus eliminating the necessity of obtaining accurate registry between an already charged sheet and .the original.

Since certain changes in carrying out the above process and in the charging apparatus set forth, which embody the invention, may be made without departing from its scope, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Y What is claimed is: 1

l. A process of producing an-electrostatic charge upon the surface of a flexible photo-conductive insulating material, which process comprises passing said photo-conductive insulating material between two cylindrical surfaces spaced close enough to each other to effect feeding of said photo-conductive insulating material passed therebetween with substantially no air gap between each side of said insulating material and the adjacent cylindrical surface, one of which cylindrical surfaces is a grounded electrically conductive surface and the other is an electrically semi-conductive surface having a resistance within the range of from 500 to 1,500 megohms per cubic centimeter, measured at 8,000 volts per centimeter, while applying a D.C. voltage of from 4,000 to 6,500 volts to said semi-conductive surface.

2. A process of producing an electrostaticcharge upon the surface of a flexible photo-conductive insulating material, which process comprises passingV said photo-conductive insulating material between two cylindricalsurfaces spaced closeenough to each other to effect feeding of said photo-conductive insulating material passed therebetween with substantially no air gap between each side of said insulating material and the adjacent cylindrical surface, one of which cylindrical surfaces is a grounded electrically conductive surface and the otheris an electrically semi-conductive surface having a resistance within the range of from 500 to 20,000 megohms per cubic centimeter, measured at 8,000 volts per centimeter, while applying a D.C. voltage of from 4,000 to 6,500- volts to said semi-conductive surface.

Carlson Sept. 12, 1944 Trump Apr. 4, 1950 (Other references on following page) 5 UNITED STATES PATENTS Oughton et al Feb. 27, 1951 Carlson Mar. 11, 1952 Jenkins Aug. 26, 1952 Carlson Ian. 6, 1953 Thomas Apr. 3, 1956 Walkup Dec. 18, 1956 

